Merge pull request #1865 from openstax/fix_role_users_migration

Fix drop RoleUsers migration so it doesn't delete everything

Author: nathanstitt

db/migrate/20190426205807_drop_role_role_users.rb

@@ -7,15 +7,17 @@ def change
         Entity::Role.reset_column_information
 
         Entity::Role.find_each do |role|
-          user_profile_id = ActiveRecord::Base.connection.execute(
+          row = ActiveRecord::Base.connection.execute(
             <<-SQL.strip_heredoc
               SELECT "role_role_users"."user_profile_id"
               FROM "role_role_users"
               WHERE "role_role_users"."entity_role_id" = #{role.id}
             SQL
           ).to_a.first
 
-          role.update_attribute(:user_profile_id, user_profile_id) unless user_profile_id.nil?
+          next if row.nil?
+
+          role.update_attribute(:user_profile_id, row['user_profile_id'])
         end
 
         Entity::Role.where(user_profile_id: nil).delete_all